Re: [ns] werid delay between enqueue and dequeue

[Tarik Alj <aljtarik@cholla.inrs-telecom.uquebec.ca>]

>Date: Thu, 6 Jul 2000 01:10:06 -0700 (PDT)
>From: Bo  Wen <bowen@mail.wsu.edu>
>X-Sender: bowen@cougar.it.wsu.edu
>To: ns-users@isi.edu
>Subject: [ns] werid delay between enqueue and dequeue
>MIME-Version: 1.0
>
>Hi, can anyone help me figure out this problem? 
>
>The following is "grepped" trace file for a particular packet.
>Why is there a small delay between enqueue and dequeue 
>(0.012394-0.0115 = 0.000894)?  Where is it from?  From queue delay?

well, yes. That's what happens when a packet gets enqueued while other packets 
are already in there...

>
>I used droptail queue, but traffic rate did not exceed the link
>bandwidth.  however, when I test some small simulation scenario,
>the enqueue and dequeue time are exactly same.  Why?

There is a limit to the precision you can obtain, if your scenario was small no 
delay probably means negligible delay, that is the delay was to small to be 
recorded, given the precision.

>
>Thanks a lot.
>
>+ 0 0 3 cbr 500 ------- 2 0.3 6.0 0 2 
>- 0.001 0 3 cbr 500 ------- 2 0.3 6.0 0 2 
>r 0.0115 0 3 cbr 500 ------- 2 0.3 6.0 0 2 
>+ 0.0115 3 4 cbr 500 ------- 2 0.3 6.0 0 2 
>^^^^^^^^^
>- 0.012394 3 4 cbr 500 ------- 2 0.3 6.0 0 2 
>^^^^^^^^^^
>r 0.022894 3 4 cbr 500 ------- 2 0.3 6.0 0 2 
>+ 0.022894 4 6 cbr 500 ------- 2 0.3 6.0 0 2 
>- 0.023394 4 6 cbr 500 ------- 2 0.3 6.0 0 2
>r 0.033894 4 6 cbr 500 ------- 2 0.3 6.0 0 2        

Tarik